1. Field of the Invention
The invention relates to a procedure for hydrogenation of coal by means of liquid phase and fixed-bed catalyst hydrogenation.
2. Discussion of the Background
DE-OS No. 26 54 635 discloses a procedure for leading a subset of the hydrogenated coal products, which leave the high-temperature separator as vapors and gases, over one or more reactors with a catalyst at a fixed location, to obtain refined oil products. This method of proceeding has the disadvantage that an input product consisting of light crude oil, medium oil, or heavy oil must be processed by the fixed-bed catalyst. Since coal oil fractions with a higher boiling point are generally much more difficult to refine than those with a low boiling point, the oil product thus obtained will show relatively high amounts of residual sulfur, oxygen and nitrogen compounds if the catalyst load is to be kept within economically manageable limits. Another disadvantage lies in the fact that this oil product consists in part of heavy oil while light crude and medium oils are generally desired for use or for further processing.
In another application of the procedure of DE-OS No. 26 54 635, the subset of vapors and gases from the high-temperature separator is made to be considerably larger than justified by the newly formed oil. A large part of the oil recycled for producing the coal paste is thereby also refined by hydrogenolysis at the fixed-bed catalyst. Unless corresponding additional reaction space with a catalyst is provided, the degree of refinement of the oil product is further reduced. By exchanging limit crude and medium oil for heavy oil, the boiling point of the oil product can be lowered in this process. However, this requires a considerable increase in machinery and power for the distillation steps and still does not improve the degree of refinement of the oil fractions.
Both applications of the DE-OS No. 26 54 635 procedure have the additional disadvantage that oils, regardless of their boiling points, must all be processed by the same catalyst, with the result that they are treated with medicore refining capabilities. However, a particularly intensive refinement and hydrogenation is generally desired, especially for the lighter fractions, in order to use them in reforming processes without additional hydrogenation step. At the same time, it is generally sufficient to hydrogenate the cycle oil for the coal paste and possibly also the medium oil part of the product with only moderate intensity, which permits a saving of hydrogen.
A procedure is disclosed in EPA No. 0 132 526 an intermediate separator operates directly behind the high-temperature separator from which the major part of the required cycle oil is removed. A second, smaller part is also produced in this procedure by treating the paste in a flash distillation system (flashing). The vapors and gases which are located behind the intermediate separator are led over a fixed-bed catalyst. For this reason, the oil product of the coal hydrogenation always consists of the oil fractions with the lowest boiling point. However, this process does not permit selective treatment of light and medium oil fractions either. Most important, however, in this process, just like in the first design application of the procedure of DE-OS No. 26 54 635, the cycle oil used for preparing the coal slurry is not refined by hydrogenation.